1. Field of the Invention
The present invention relates to a bending press for bending sheet panels and in particular to a bending press in which the lateral length of a blank holding device provided therein is adjustable in accordance with the width of the sheet panel to be bent.
2. Prior Art
Sheet panels which have folded flanges are used very extensively in the manufacture of household electrical appliances, tool cases, furniture and metallic shelving. The manufacture of these sheet panels is carried out with suitable bending presses or folding presses, the main elements of which are an assembly of blades and a blank holding device, the action of which produces desired bending or folding on the planar sheets such as sheet metal fed to the bending press.
At the present state of the art, there are known some bending presses in which a pair of blades are supported, opposite one to the other, by a cutter block shaped as a "C" and movable in the vertical direction with respect to a blank holding device.
In the case in which panels with flanges folded towards the interior are produced, the blank holding device must be capable of undergoing contraction in order to allow the release of the sheet panel from the blank holding device. In addition, there must be the possibility of varying the width of the same blank holding device in accordance with the change of the width of the panels and the profile of the bending to be formed on the panels.
According to the present state of the art, there is known a bending press capable of modifying in a programmed manner the length of the blank holding device (for example, U.S. Pat. No. 4,856,315 and JP 7-112215 A). The variation of the length of the blank holding device is achieved in the conventional apparatuses mainly by varying the number of the suitable segments included therein. The final adjustment of the length of the blank holding device is then carried out, for example, by substitution of the extremity members of the blank holding device. Such conventional press is provided on the side of the blank holding device with two storehouses each containing a plurality of the symmetrically corresponding extremity members and means for carrying out automatic and programmed substitution of the extremity members. The storehouse consists of programmed carriages provided with separation systems which slidable along guides by means of the rotation of screws having the same length as the guides. The screws is placed in motion by suitable motors in the two directions. The motion of the carriages for achieving the substitution of the extremity members must occur contemporaneously and must be synchronized with the contraction of the blank holding device.
The conventional bending press has the drawback that it is functionally limited due to its complexity. An example of such drawback is that the cost of administration and maintenance is increased. The considerable dimension and consequently the space occupied by the conventional apparatuses is another problem. By way of summary, the limitations of the conventional apparatuses are as follows:
1) Two storehouses each containing a plurality of devices are needed, which increase the cost of the bending press and requires considerable space; PA1 2) Excessive machinery for hooking and unhooking the extremity members is needed, which causes mechanical problems and increases the maintenance costs; PA1 3) The change of the extremity members must be carried out only at a fixed vertical position of the blank holding device with respect to the front plate of the apparatus, which is vertically fixed.